Low-temperature magnetic ordering in SrEr2O4

SrEr2O4 has been characterized by low-temperature powder neutron diffraction, as well as single-crystal specific-heat and magnetization measurements. Magnetization measurements show that the magnetic system is highly anisotropic at temperature above ordering. A magnetic field of 280 kOe applied at T=1.6 K does not overcome the anisotropic magnetization and fails to fully saturate the system. Long-range antiferromagnetic ordering develops below T-N=0.75 K, identified by magnetic Bragg reflections with propagation vector k=0 and a lambda anomaly in the specific heat. The magnetic structure consists of ferromagnetic chains running along the c axis, two adjacent chains being stacked antiferromagnetically. The moments point along the c direction, but only one of the two crystallographically inequivalent Er sites has a sizeable ordered magnetic moment, 4.5 mu(B) at 0.55 K. The magnetic properties of SrEr2O4 are discussed in terms of the interplay between the low dimensionality, competing exchange interactions, dipolar interactions, and low-lying crystal-field levels.